A Survey of Morphological Variation in Adult Meristogenys Amoropalamus (Amphibia, Anura, Ranidae), with a Description of a New Cryptic Species
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Zootaxa 2905: 33–56 (2011) ISSN 1175-5326 (print edition) www.mapress.com/zootaxa/ Article ZOOTAXA Copyright © 2011 · Magnolia Press ISSN 1175-5334 (online edition) A survey of morphological variation in adult Meristogenys amoropalamus (Amphibia, Anura, Ranidae), with a description of a new cryptic species TOMOHIKO SHIMADA1, 2, MASAFUMI MATSUI2,5, PAUL YAMBUN3 & AHMAD SUDIN4 1Department of Science, Faculty of Education, Aichi University of Education, Kariya, Aichi 448-8542, Japan 2Graduate School of Human and Environmental Studies, Kyoto University, Sakyo, Kyoto 606-8501, Japan 3Research and Education Division, Sabah Parks, P. O. Box 10626, Kota Kinabalu 88806, Sabah, Malaysia 4Institute for Tropical Biology and Conservation, University Malaysia Sabah, Kota Kinabalu 88999, Sabah, Malaysia 5Corresponding author. E-mail: [email protected] Abstract Previous analyses of molecular and larval morphology have suggested that Meristogenys amoropalamus is composed of two cryptic species, but no diagnostic characters of their adult morphology have been reported. Here, we compared adult characters of these two species and found that they differed in iris colour (yellowish-green and sandy brown), tympanum size and relative limb length. Based on the results of analysis of DNA sequences of the type specimens and a discriminant analysis using 18 morphological variables, we conclude that the lineage with green irises is the true M. amoropalamus, and that the lineage with sandy brown irises is a new species, M. dyscritus sp. nov. In northern Sabah, M. dyscritus is dis- tributed in altitudes lower than those of M. amoropalamus, but the distributional ranges of their larvae overlap in some streams. Meristogenys amoropalamus has larger and lighter-coloured ova, smaller clutch sizes and a more interstitial lar- val life than M. dyscritus. These differences suggest that M. amoropalamus has a more cryptic life during its larval period than M. dyscritus. Key words: trade-off of reproductive traits, iris color, Borneo, cryptic species, Meristogenys Introduction In many phylogenetically related species of frogs, tadpoles are more difficult to separate than adults (Inger & Stue- bing, 2005), but the reverse is true in some species such as Bufo japonicus and B. torrenticola (Matsui, 1976). The Bornean endemic ranid genus Meristogenys represents one such unusual case (Inger & Stuebing, 2005). Larvae of this genus are specialised for a life in strong currents, with a large mouth on the underside of the snout and a large abdominal sucker covering the abdomen. In contrast to adults, which usually have few notable inter-specific differ- ences in external morphology, these larvae possess many taxonomically useful characters, such as their labial tooth raw formula (LTRF), jaw sheath shape, and presence or absence of surface projections and dermal glands (Shimada et al., 2007a). This tendency is obvious in the two cryptic forms found in Meristogenys amoropalamus sensu lato. Shimada et al. (2007a, 2008) found two larval forms (morphotypes 1 and 3-a) in M. amoropalamus sensu lato that were differ- entiated by mitochondrial (mt) and nuclear DNA (nuDNA) sequence characters. These two forms were considered to represent distinct species, but no taxonomic decision was made because they were not easily differentiated by adult morphology and no evidence existed to determine which of the two forms is the true M. amoropalamus. To resolve this taxonomic problem, we searched for diagnostic morphological characters that distinguish adult specimens. We also studied sequences of DNA fragments from the type specimens of M. amoropalamus and com- pared them with the larval sequences. Based on our results, we describe a new species and discuss the distribution and reproductive traits of the new form compared to those of M. amoropalamus. Accepted by M. Vences: 11 May 2011; published: 3 Jun. 2011 33 Material and methods Specimen sampling. Following Matsui’s (1986) description, we used 97 adult specimens (68 males and 29 females) morphologically identified as M. amoropalamus. However, not all specimens strictly fit Matsui’s key (Matsui, 1986). For example, even when a specimen had more highly developed toe webbing than that described by Matsui (1986), it was identified as M. amoropalamus based on all the other characters diagnostic for this spe- cies. We followed the procedure of Shimada et al. (2007a) to fix and preserve specimens and to determine sex and maturity. Specimens were collected from five localities in Sabah (Kamborangah, Liwagu, Mahua, Mesilau, and Wario) and one locality in Sarawak (Bario) (Fig. 1). We also examined three type specimens of M. amoropalamus collected from the type locality [Sg. (Sungai, meaning “river”) Pa Riman, Gn. (Gunung, meaning “mountain”) Tapai Sia, Krayan County, East Kalimantan, Indonesia; alt. 1300 m] and Liwagu (Liwagu River, 1500 m, head- quarters of Kinabalu National Park) (Matsui, 1986). For the larval description, we examined specimens from Bundu Tuhan, Liwagu, Mahua, Mesilau, Poring and Wario (Fig. 1). A part of these specimens had been molecu- larly identified to either of the two lineages of M. amoropalamus sensu lato by Shimada et al. (2008), based on DNA sequences extracted from tissue samples collected before formalin fixation. Molecular identification. For all samples except for the type specimens, we extracted DNA, amplified approximately 440 base pair (bp) fragments of mitochondrial 12S rRNA using the primers L1091 and Hnew (Shi- mada et al., 2011) and determined the sequences following the protocol of Shimada et al. (2008). Although a variety of methods has been proposed for the extraction of DNA from formalin-fixed specimens, some of them are known to have no effects, or even a harmful effects for the quality of extracted DNA (Gilbert et al., 2007). We adopt the phenol-chloroform extraction after the digestion with optimal temperature and long (48 h) duration, because this method was most similar to our original protocol among the methods which Gilbert et al. (2007) had confirmed the effectiveness. Under the allowance of the curator of Osaka Museum of Natural History (OMNH), we cut a small piece (3 mm x 10 mm) of muscle from the abdominal wall, and ground it with a plastic pestle in 600 µl of STE buffer (0.1M NaCl; 0.05M Tris-HCl, pH 7.5; 0.001M EDTA) in a 1.5 ml tube. After the addition of 60 µl of 10% SDS and 15 µl of 10 mg/ml proteinase K solution, we kept it in an incubator at 55 °C for 36–72 hours (we continued the digestion until the visible tissue completely disappears). During the digestion, we sometimes tapped the tube calmly, and added 15 µl of proteinase K solution twice. After the digestion, we added TE saturated phenol with the same amount of the sample solution, mixed it with a electric shaker for 10 min, and centrifuged them (7500 rpm, 10 min, room temperature). The upper layer (water layer) was washed once in phenol- chloroform-isoamylalcohol (PCI) and once in chloroform-isoamylalcohol (CIA) in the same way as the phenol. After the phenol-chloroform washes, we obtained a pellet of DNA through the ordinary ethanol precipitation (addi- tion of 45 µl of 5M NaCl solution and 900 µl of 99.5% ethoanol; 10 min incubation; centrifuge with 14,000 rpm, 20 min, and 4 °C). The pellet was dissolved in 100 µl of TE buffer (10mM Tris-HCl, 1mM EDTA, pH 8.0). We added two drops of sterile mineral oil to prevent the solution from evaporation. To examine the quality of extracted DNA, we applied 2 µl of the solution to an agarose gel, and compare the result of electrophoresis with others. As we found that the DNA extracted from formalin fixed specimens was shorter than others (data not shown), we divided the mtDNA region into four fragments, and prepared two primers for each of them (L1091, Hnew, L1173: AACCCAAAGGACTTGACGGT, L1264: TCAGTCTGTATACCTCCGTCG, L1371: AAGAAATGGGCTA- CAATTTCTA, H1243: GAGGTATACAGACTGATTAGG, H1352: TAGAAATTGTAGCCCATTTCTT, and H1471: TGACGGGCGGTGTGTACGCG). The polymerase chain reaction (PCR) cycle included an initial dena- turation for 1 min at 94°C, 60 cycles of denaturation for 20 s at 94°C, primer annealing for 20 s at 45°C, extension for 40 s at 72°C and a last extension for 3 min at 72°C. As the PCR buffer, we used Ampdirect (Shimadzu Co.) for unpurified DNA. To avoid contamination, we separated all reagents, tubes, and extracted samples from those of other experiments, and conducted negative-control experiments for all procedures involving the type specimens. The sequences used in this paper were deposited in GenBank (AB359966–AB360009, AB360012–AB360018, AB360020–AB360043 and AB617705–AB617726). We compared the adult sequences with those of known sequences of the larval morphotypes 1 and 3-a (AB262538 for morphotype 1 and AB262541 and AB262542 for morphotype 3-a). The genetic distances between these two morphotypes were 4.5%–4.7% [Kimura’s two-parameter (K2p) distances] (Kimura, 1980) in this region of 12S rRNA (Shimada et al., 2007a). The larval morphotype 3-a is known to contain two distantly separate mtDNA lineages, but we treated them as a single taxon because no morphological or nuDNA differences between 34 · Zootaxa 2905 © 2011 Magnolia Press SHIMADA ET AL. them have been found (Shimada et al., 2008). We called adults of larval morphotype 1 “Group A” and those of morphotype 3-a “Group B”. We considered a genetic (K2p) distance less than 1.1% as intra-specific because Shi- mada et al. (2007a) reported intra-specific genetic distances of Meristogenys to range from 0% to 1.1% in this frag- ment. FIGURE 1. Map of Borneo showing the localities discussed in this study. 1, Wario; 2, Bundu Tuhan; 3, Liwagu; 4, Kamboran- gah; 5, Mesilau; 6, Poring; 7, Mahua; 8, Bario; 9, Gunung Tapai Sia. KNP and CRNP indicate Kinabalu National Park and Crocker Range National Park, respectively. Closed and open dots indicates the sampling localities of Group A (Meristogenys amoropalamus) and Group B (M.